Call size feedback on PNNI operation

ABSTRACT

The invention provides a method and system for selecting routes in a switching network with resource reservation, such as an ATM network. A set of routes are periodically precomputed, so that routes are known between any sending node and any receiving node, subject to resource reservation requirements. Each incoming call has its resource requirements, such as call size, compared with a selected threshold, and if the requirements exceed the threshold, a route is dynamically recomputed for the call. Other aspects of routing may be responsive to the calls&#39; resource requirements. For example, a ratio of required resources with quality-of-service restrictions to required resources without such restrictions may be used to determine whether to reject the call, responsive to the call&#39;s resource requirements. The call size may be compared against another selected threshold, and the decision to determine whether to use that ratio to reject the call may be made responsive to comparisons against one or both thresholds.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to ATM networks.

2. Related Art

In known ATM systems, different calls can have different requirementsfor transmission bandwidth. The transmission bandwidth requirement for acall is termed its "size." For example, a videoconference call isconsidered "larger" than a simple voice call. When selecting a virtualcircuit for routing each call in an ATM network, the size of the call isconsidered in determining which switching nodes to select for routingeach call or which through, or if the call should be rejected due to alack of transmission capacity.

Known ATM systems determine the route for the virtual circuit for eachincoming call as the call enters the ATM network. However, one problemwhich has arisen in the art is that this operation requires substantialcomputation. Accordingly, while this method achieves the goal ofdetermining the virtual circuit for each incoming call, it has thedrawback of requiring substantial resources for computation, can delayprocessing of incoming calls, and can therefore result in lesserthroughput of incoming calls by the ATM system.

One technique to reduce the computation intensity associated with routecomputation is to use precomputed routes. However, precomputed routescan produce paths that are less efficient from the point of view ofbandwidth utilization than routes computed dynamically. It would beadvantageous to dynamically route those calls which might have asignificant impact on overall bandwidth utilization in the network.

Accordingly, it would be desirable to provide a method and system forselecting routes in an ATM network, which does not require excessivedynamic route computation. This advantage is achieved in an embodimentof the invention in which most routes are precomputed, but some routesare dynamically computed in response to call size, thus call size isused to determine or help determine whether a dynamically computed routeshould be used instead of a precomputed route.

SUMMARY OF INVENTION

The invention provides a method and system for selecting routes in aswitching network with resource reservation, such as an ATM network. Aset of routes are periodically precomputed, so that routes are knownbetween any sending node and any receiving node, subject to resourcereservation requirements (such as call size). Each incoming call has itsresource requirements, such as call size, compared with a selectedthreshold, and if the requirements exceed the threshold, a route isdynamically recomputed for the call.

In alternative embodiments, other aspects of routing may also beresponsive to the calls' resource requirements (such as call size). Forexample, a ratio of required resources with quality-of-servicerestrictions to required resources without such restrictions may be usedto determine whether to reject the call, responsive to the call'sresource requirements. In such alternative embodiments, the call sizemay be compared against another selected threshold, and the decision todetermine whether to use that ratio to reject the call may be maderesponsive to comparisons against one or both thresholds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process flow diagram of a method for selecting routes ina switching network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, a preferred embodiment of the invention isdescribed with regard to preferred process steps and data structures.Those skilled in the art would recognize after perusal of thisapplication that embodiments of the invention can be implemented usinggeneral purpose switching processors or special purpose switchingprocessors or other circuits adapted to particular process steps anddata structures described herein, and that implementation of the processsteps and data structures described herein would not require undueexperimentation or further invention.

Inventions described herein can be used in conjunction with inventionsdescribed in the following application:

Application Ser. No. 08/862,915, filed May 23, 1997, Express Mailing No.EM302071674, in the name of the same inventors, titled "Next HopSelection in ATM Networks", having attorney docket number CIS-025.

This application is hereby incorporated by reference as if fully setforth herein.

Precomputed Routes or Dynamic Recomputation

FIG. 1 shows a process flow diagram of a method for selecting routes ina switching network.

A method 100 for selecting routes in a switching network includes theflow points 110 through 170, and steps therebetween. The method 100 ispreferably performed in a switching network with resource reservation,such as an ATM network.

At a flow point 110, the switching network includes a set of nodes,including at least one sending node, at least one receiving node, and aplurality of routes between the sending nodes and the receiving nodes.

At a step 121, the method 100 precomputes a set of routes between eachof the sending nodes and each of the receiving nodes, subject toresource reservation requirements.

The step 121 is periodically performed, so that precomputed routes areknown between any of the sending nodes and any of the receiving nodes,and the routes which are known are subject to resource reservationrequirements.

As used herein, the concept of "precomputed" routes includes schemes inwhich a set of routes, or a set of preferred routes, are determinedindependent of parameters of the call. This includes cases where someprecomputed routes are in fact computed or partially computed at or nearthe time the call arrives, but are determined independent of parametersof the call such as call size. A fixed technique for determining apreferred route is a precomputed route, while a technique or selectionamong techniques which is responsive to the call size and determinesdifferent routes for calls having different sizes (as opposed to merelyrejecting calls which are too large) is not a precomputed route.

At a flow point 130, an incoming call arrives at one of the sendingnodes. The incoming call includes a designated receiving node and a setof resource requirements. For example, one such resource requirement isa call size for the incoming call.

The incoming call is preferably an incoming call in a telephone networkto be routed using the ATM network.

At a step 141, the call size for the incoming call is compared with afirst selected threshold. In a preferred embodiment, the first selectedthreshold is a static value set by an operator using a networkmanagement system for a peer group in the ATM network. For example, thestatic value may comprise a value such as about 1 megabit per second, ora value such as about 384 kilobits per second, so as to distinguishbetween ordinary voice telephone calls and videotelephone calls. Inalternative embodiments, the first selected threshold may be dynamicallydetermined in response to traffic in the ATM network or other factors.For example, the first selected threshold may be determined in responseto the number and type of call requests received, so as to approximatelylimit the number of calls for which routes are dynamically computed to aselected limit.

At a step 142, if the call size for the incoming call exceeds the firstselected threshold, the method 100 dynamically recomputes a route forthe call (thus disregarding the precomputed routes). Otherwise, themethod 100 does not perform the step 142.

Call Rejection For Excessive Resource Usage

At a step 143, the call size for the incoming call is compared with asecond selected threshold. In a preferred embodiment, the secondselected threshold is a static value; however, in alternativeembodiments, the second selected threshold may be determined responsiveto traffic in the ATM network or other factors, in similar manner as thefirst selected threshold is determined in the step 141.

At a step 144, if the call size for the incoming call does not exceedthe second selected threshold, the method 100 continues with the flowpoint 150. Otherwise, the method 100 proceeds to determine anexcess-usage ratio of required resources with quality-of-servicerestrictions to required resources without such restrictions.

To determine the ratio in the step 144, the method 100 performs thefollowing sub-steps:

At a sub-step 144(a), the method 100 determines a first route for theincoming call without using quality of service restrictions.

At a sub-step 144(b), the method 100 determines a first weighted hopcount n0 for the first route.

In a preferred embodiment, the first weighted hop count is computed byassigning a relatively lower administrative cost to relativelyhigher-speed interfaces. For example, the administrative cost for a hopcan be inversely proportional to the total Maximum Cell Rate ofinterfaces available for that hop.

At a sub-step 144(c), the method 100 determines a second route for theincoming call, this time using quality of service restrictions.

The second route can require different switching nodes and can requiremore switching nodes than the first route, because quality of servicerestrictions restrict the nature of the interfaces through which thecall can pass.

At a sub-step 144(d), the method 100 determines a second weighted hopcount n1 for the second route.

In a preferred embodiment, the second weighted hop count is determinedin like manner as the first weighted hop count. Thus, the secondweighted hop count is computed by assigning a relatively loweradministrative cost to relatively higher-speed interfaces.

At a sub-step 144(e), the method 100 determines the excess-usage ration1/n0.

At a step 145, if the excess-usage ratio n1/n0 determined in the step144 exceeds a third selected threshold, the method 100 rejects the call.

In a preferred embodiment, the third selected threshold is a staticvalue; however, in alternative embodiments, the third selected thresholdmay be determined responsive to traffic in the ATM network or otherfactors, in similar manner as the first selected threshold is determinedin the step 141. In a preferred embodiment, the third selected thresholdis an excess-usage ratio of about 1.5 to 1 for a relatively densenetwork, or about 2 or 3 to 1 for a relatively sparse network.

At a flow point 150, a route is known for the incoming call.

At a step 161, the incoming call is routed according to the known route.

At a flow point 170, the method 100 is complete.

Further Applicability of Resource Requirement Feedback

The resource requirements of the incoming call has broader applicabilitythan determining (a) whether to dynamically recompute routes, or (b)whether to dynamically determine an excess-usage ratio and rejectincoming calls responsive thereto.

For example, the method 100 can determine, responsive to the resourcesrequired by the incoming call (such as call size), whether to applytechniques relating to one or more of the following:

In a dynamic path recomputation protocol, such as in virtual path andvirtual circuit recomputation, the call size can be used to determinefor which calls to determine whether to reroute paths. For example,paths can be dynamically rerouted only for those calls which are largeenough to make a significant difference.

In a system which transmits multicast information, the call size can beused to determine for which point to multipoint calls to attempt tooptimize (or partially reoptimize) the multicast routing tree.Similarly, in a system which transmits multicast information and alsoreceives point to point calls, the call size can be used to determinefor which newly arrived calls to trigger an attempt to optimize (orpartially reoptimize) multicast routing trees.

In other routing protocols which concern or involve dynamic pathcomputation or resource reservation, the call size can be used todetermine for which calls to attempt to perform dynamic path computationor resource reservation.

Alternative Embodiments

Although preferred embodiments are disclosed herein, many variations arepossible which remain within the concept, scope, and spirit of theinvention, and these variations would become clear to those skilled inthe art after perusal of this application.

What is claimed is:
 1. A method, including the steps ofprecomputing aset of routes in a switching network, said routes being between aplurality of sending nodes and a plurality of receiving nodes; receivinga request for a virtual circuit at one of said sending nodes, saidrequest including a designated receiving node; examining a set ofresource requirements for said request; and choosing whether todynamically compute a new route between said one sending node and saiddesignated receiving node, responsive to whether any of said set ofresource requirements exceeds a set of selected thresholds, saidthresholds determined in response to a network parameter.
 2. A method asin claim 1, wherein said switching network is an ATM network.
 3. Amethod as in claim 1, wherein said request comprises an incoming call ina telephone network.
 4. A method as in claim 1, wherein said resourcerequirements include a call size.
 5. A method as in claim 1,wherein:said resource requirements include a call size; and said step ofchoosing includes the step of comparing said call size with a selectedthreshold.
 6. A method, including the steps ofreceiving a request for avirtual circuit in a switching network, said network having a pluralityof sending nodes and a plurality of receiving nodes, said request beingreceived at a sending node; examining a set of resource requirements forsaid request; and choosing whether to dynamically compute a ratio ofrequired resources with quality-of-service restrictions to requiredresources without such restrictions, responsive to whether any of saidresource requirements exceeds a set of selected thresholds, saidthresholds determined in response to a network parameter.
 7. A method asin claim 6, wherein said switching network is an ATM network.
 8. Amethod as in claim 6, wherein said request comprises an incoming call ina telephone network.
 9. A method as in claim 6, wherein said resourcerequirements include a call size.
 10. A method as in claim 6,wherein:said resource requirements include a call size; and said step ofchoosing includes the step of comparing said call size with a selectedthreshold.
 11. A method as in claim 6, comprising the step ofdetermining whether to reject said request, responsive to saiddynamically computed ratio.
 12. A node in a switching network, said nodeincluding:a periodic route determination mechanism configured toperiodically precompute a set of routes in said switching network, saidset of routes including a plurality of sending nodes and a plurality ofreceiving nodes; a receiver mechanism configured to receive a requestfor a virtual circuit including a designated receiving node; adetermination mechanism configured to examine a set of resourcerequirements for said request received by the receiver mechanism; and adecision mechanism configured to choose whether to dynamically compute anew route between said node and said designated receiving node,responsive to whether any of said set of resource requirements exceeds aset of selected thresholds, said thresholds determined in response to anetwork parameter.
 13. The node of claim 12, wherein said switchingnetwork is an ATM network.
 14. The node of claim 12, wherein saidrequest comprises an incoming call in a telephone network.
 15. The nodeof claim 12, wherein said resource requirements include a call size. 16.The node of claim 12, wherein:said resource requirements include a callsize; and the decision mechanism includes a comparison mechanismconfigured to compare said call size with a selected threshold.
 17. Asystem including:a switching network having a plurality of sending nodesand a plurality of receiving nodes, one of said plurality of sendingnodes being a designated sending node and one of said plurality ofreceiving nodes being a designated receiving node; a receiver mechanismconfigured to receive a request for a virtual circuit on said network,said receiver mechanism in communication with at least one of saiddesignated sending node and said designated receiving node; adetermination mechanism configured to examine a set of resourcerequirements for said request, said determination mechanism incommunication with the receiver mechanism; and a decision mechanismconfigured to choose whether to dynamically compute a ratio of requiredresources with quality-of-service restrictions to required resourceswithout such restrictions, responsive to whether any of said resourcerequirements exceeds a set of selected thresholds, said thresholdsdetermined in response to a network parameter, said decision mechanismin communication with said determination mechanism.
 18. The system ofclaim 17, wherein said switching network is an ATM network.
 19. Thesystem of claim 17, wherein said request comprises an incoming call in atelephone network.
 20. The system of claim 17, wherein said resourcerequirements include a call size.
 21. The system of claim 17,whereinsaid resource requirements include a call size; and the decisionmechanism includes a comparison mechanism configured to compare saidcall size with a selected threshold.
 22. The system of claim 17, furtherincluding a rejection mechanism configured to determine whether toreject said request, responsive to said dynamically computed ratiocomputed by the decision mechanism.
 23. An object-oriented softwaresystem for selecting routes in a switching network with resourcereservation said software system comprising:an object for receiving arequest for a virtual circuit in a switching network, said networkhaving a plurality of sending nodes and a plurality of receiving nodes,said request being received at a sending node; an object for examining aset of resource requirements for said request; and an object forchoosing whether to dynamically compute a ratio of required resourceswith quality-of-service restrictions to required resources without suchrestrictions, responsive to whether any of said resource requirementsexceeds a set of selected thresholds, said thresholds determined inresponse to a network parameter; wherein a set of actions carried out inoperation of said software system are as depicted in the flow diagram ofFIG.
 1. 24. A software system as in claim 23, wherein said switchingnetwork is an ATM network.
 25. A software system as in claim 23, whereinsaid request comprises an incoming call in a telephone network.
 26. Asoftware system as in claim 23, wherein said resource requirementsinclude a call size.
 27. A software system as in claim 23, whereinsaidresource requirements include a call size; and said step of choosingincludes the step of comparing said call size with a selected threshold.28. A software system as in claim 23, comprising the step of determiningwhether to reject said request, responsive to said dynamically computedratio.